This week's poem comes from Amy Lowell's second collection, Sword Blades and Poppy Seed (1914). It was the book in which she found her characteristic style. Her first, A Dome of Many-Coloured Glass (1912) was heavily coloured by the English Romantic poets, especially Keats, whose biographer she later became. The discovery of the imagist poet HD, whose work was published in Harriet Monroe's magazine, Poetry, in 1913, was the most important catalyst in her development.

From the French symbolist poet Paul Fort she learned a technique of writing "polyphonic prose" – prose which used the different voices of poetry, such as "metre, vers libre, assonance, alliteration, rhyme and return". This, too, had an all-round liberating effect. And not least was her deepening relationship with the actress Ada Russell. "In a Garden" is one of the many love poems Amy wrote for the woman who would became her life-long partner. These sensuous and boldly unguarded expressions of lesbian eroticism range from the explicit "The Weather-Cock Points South" to rhapsodic muse-poems like "In Excelsis", and are startlingly ahead of their time. They represent Lowell's most substantial and original achievement.

Her enthusiasm for imagism took her to England, where she established an association with Ezra Pound and his circle. He accepted one of her poems for the first imagist anthology: then Amy took over the "brand" and the funding. She became imagism's ambassador, and edited the three subsequent anthologies. Pound objected to her "democratising" aesthetic, and rebuffed her with the famous taunt of "Amy-gism". A more sympathetic commentator, Harriet Monroe, wrote, "The force which Miss Lowell's New England ancestors put into founding and running cotton mills, or belike into saving souls, she puts into conquering art and making it express and serve her."

"In a Garden" is both sensuous and subtle, as carefully shaped for sound effects as for imagery. The feminine symbolism of flowing, opulent water is introduced by a chain of extended relative clauses. "Gushing from the mouths of stone men," the water doesn't appear until line six. These stone men are presumably the figures of the fountains, their gargoyle-like faces spewing water, but the phrase also evokes an opposed, masculine resistance. The image of "Granite-lipped basins" furthers the association. The water, by contrast, is "spread at ease under the sky", and even the irises seem playful: they "dabble their feet/And rustle to a passing wind". The preposition "to" in preference to the expected "in" suggests a kind of flirtatiousness, as if the flowers were female dancers, the wind their partner. And already the sound of the water has been conjured in the verbs, "dabble" and "rustle".

The hyperbaton in the second stanza is carefully judged, reversing the usual syntactical hierarchy and ensuring the most significant words come first. The sound of the water and the gently elated mood register through repetition. "Stone" in line eight echoes the poem's opening. The "fountains" of line nine become "marble fountains" in the next. The word "water" appears in every segment of the poem, three times forming a line's feminine ending.

The softness of "moss-tarnished" steps, connected to the damp, ferny tunnels, contrasts with the crisper clarity of "gurgling" and "leaping", the latter verb both visual and auditory. Lowell chooses unremarkable words, words often associated with the description of water. But they have precise, and clearly separate effects, and are combined in a wonderfully realised polyphonic soundscape.

Stanzas one to three are important but introductory: they set the scene for the emotional and narrative crux that lies in waiting, and now occupies the remainder of the poem, beginning, "And I wished for night and you." The tone is not necessarily one of disappointment or loss. "I wanted to see you in the swimming-pool" may express simply that, a desire, and an imagined happiness to be fulfilled. The brightness of moonlight touches water and naked flesh, and the bathing woman herself becomes moonlike. Lowell's romanticism is both conventional and unconventional: the moonlit woman is not a nymph, after all, but a real woman in a swimming-pool. The lilacs, too, remind us we're in an ordinary though transformed garden. The beautifully-paced last line summarises and completes the imagined scenario, but leaves the poem still in motion, ending as it began, with the present participle of a verb.

"I do not believe it is what one says in a poem that matters," Lowell wrote to Richard Aldington, "It is the kind of light that plays over it." This perhaps suggests an impressionistic technique rather than the hard clear focus of imagism. "In a Garden" is imagist in its "direct treatment of the thing" and in the musicality of its phrasing. If it contravenes the strict interpretation of the imagist dictum "to use no word that does not contribute to the presentation", the writer would surely argue that the repetitions are vital to the presentation of her poem in all its sensuous variety. And we would have to agree with her.

In a Garden

Gushing from the mouths of stone menTo spread at ease under the skyIn granite-lipped basins,Where iris dabble their feetAnd rustle to a passing wind,The water fills the garden with its rushing,In the midst of the quiet of close-clipped lawns.

Damp smell the ferns in tunnels of stone,Where trickle and plash the fountains,Marble fountains, yellowed with much water.

Splashing down moss-tarnished stepsIt falls, the water;And the air is throbbing with it.With its gurgling and running.With its leaping, and deep, cool murmur.

And I wished for night and you.I wanted to see you in the swimming-pool,White and shining in the silver-flecked water.While the moon rode over the garden,High in the arch of night,And the scent of the lilacs was heavy with stillness.